Sugarcane yield and soil properties as influenced by organic and inorganic fertilisers

Field experiments were conducted on a Vertisol soil to evaluate the effect of organic matter, inorganic fertilisers and their combination on cane and sugar yield and their effect on soil properties. The main-plot treatments consisted of two rates of mill mud, PM1 and PM2 (12.5 and 25.0 t/ha, respectively), two rates of bio-compost (a blend of mill by-products with microbial culture called bio-compost), BC1, BC2 (2.5, 5.0 t/ha, respectively), and a control (no mill mud or bio-compost). Four rates of inorganic fertilisers were determined from the recommended dose of fertiliser (RDF) were used as sub-plot factors, 100% (RDF1), 75% (RDF2), 50% (RDF3) and 0% (RDF4), in a split-plot design with four replicates. Pooled data indicated that the application of bio-compost at 5 t/ha and mill mud at 25 t/ha significantly increased cane yield to 101.9 t/ha and 91.0 t/ha, respectively, over the control (80.3 t/ha). However, lower doses of these organics failed to produce significant yield increases over that of the control. Integrating bio- compost with 100 and 75% RDF produced significantly higher cane yield. Bio-compost at 5 t/ha along with 75% RDF produced yields on par with 100% RDF alone, allowing a 25% saving in RDF as well as improving cane yields. Higher yield responses due to bio-compost across various rates of inorganic fertilisers and other organic fertilisers are attributed to better nutrient content and the impact on soil biota. All organics tended to increase significantly the organic carbon, available nitrogen, phosphorus and potassium in the soil. The organics also increased the population of the P-solubilisers Azotobacter, Actinomycetes and fungi. Microbial counts were significantly higher at fertilizer rates of 100% RDF than at lower rates. It is concluded that a combination of organic and inorganic fertilisers helps to achieve the improved soil properties as well as increasing the cane yields. The superior effect of bio-compost over mill mud in obtaining higher cane and sugar yields was attributed to higher nutrient content of bio-compost and its positive effect on soil microbes. Key words Bio-compost, mill mud, P-solubilisers, fertilisers